1. Field of the Invention
The present invention generally relates to a lens which is movably positioned along a guide rod, and in particular relates to a movably positioned lens having magnetic means for holding it in place on the guide rod.
2. Description of the Prior Art
Conventional guidance assemblies for optical or mechanical devices include guide rods and re-circulating linear ball bearings which must be heavily pre-loaded to provide precision play-free guidance. This results in high cost, requires high accuracy between mating pans, and includes relatively bulky components.
Further, relatively high drive forces are typically needed to move the pre-loaded components. Such pre-loads are susceptible to change with temperature.
In one typical use, a guidance assembly supports a lens for filming motion pictures which requires exceptionally accurate positioning to ensure very sharp images to film a master tape (from which all future tapes will be copied). The filming of a motion picture may subject the guidance assembly to extreme temperature variations, such as those in a desert or mountainous climate. The extreme temperature variations may cause difficulty in positioning the lens assembly and may cause movement due to expansion and contraction in a pre-positioned lens assembly.